This invention relates to a device for providing mechanical support to a vessel lumen of a living being.
A variety of medical situations requires the use of a mechanism to expand and support a constricted vessel and to maintain an open passageway through the vessel. A few examples of such situations following angioplasty include holding a dissection in place, preventing closure during spasm, and preventing acute closure due to thrombosis. In these situations, devices, commonly known as stents, are useful to prevent stenosis of a dilated vessel, or to eliminate the danger of occlusion caused by "flaps" resulting from intimal tears that may be associated with angioplasty, or to hold two ends of a vessel in place.
Stents have been made using materials of varied composition and conformation. McGreevy et al U.S. Pat. Nos. 4,690,684 and 4,770,176 describe a meltable stent that is inserted into the interior of the ends of a blood vessel during anastomosis. Anastomosis refers to the surgical or physical connection of two tubular structures, such as veins or arteries. The stent is made of blood plasma, which is biologically compatible with the living being and which melts rapidly in response to heat.
The Fischell et al U.S. Pat. No. 4,768,507 describes an intravascular stent which is an unrestrained coil spring having an outside diameter of 2 to 12 millimeters and a length of 5 to 25 millimeters. The materials of construction are stainless steel, and a titanium alloy. Decreased thrombogenicity is achievable by coating the outside of the coil with a non-thrombogenic material such as ULTI carbon.
The Leeven et al U.S. Pat. No. 4,820,298 describes a stent having a flexible tubular body made from a thermal plastic to the form of a helix. Polyester and polycarbonate copolymers are selected as particularly desirable materials.
The Wolff et al U.S. Pat. No. 4,830,003 describes a stent made from wires formed into a cylinder. The wires are made of a biocompatible metal. Biocompatible metals include 300 series stainless steels such as 316 LSS, as well as platinum and platinum-iridium alloys, cobalt-chromium alloys such as MP35N, and unalloyed titanium.
The Wiktor U.S. Pat. No. 4,886,062 describes a stent made from low memory metal such as a copper alloy, titanium, or gold. The stent is preformed into a two-dimensional zig-zag form creating a flat expandable band.
The Gianturco U.S. Pat. No. 4,907,336 describes a wire stent having a cylindrical shape that results from an expandable serpentine configuration. Malleable materials of construction are preferably included from the group of annealed stainless steels, tungsten and platinum.
Goldberg et al, Canadian Application 2,025,626, describe a bio-degradable infusion stent used to treat ureteral obstructions. The application describes an extruded material of construction made of epsilon-caprolactone (15-25% w/w of terpolymer composition); glycoside (5-50% w/w) and L(-)lactide (45-85% w/w). This material was described as having a minimum tensile strength of at least 500 pounds per square inch, preferably 650 psi; elongation of greater than 10%, preferably greater than 100%; and Shore A hardness equal to 50-100%, preferably 75-95%. The Goldberg et al patent application describes a method for incorporating radiopaque materials such as barium sulfate into the polymer in amounts ranging from 5-30%. The mechanism of biodegradation is described as hydrolysis resulting in degradable products excreted in urine or reabsorbed into tissues. The duration of functional life of the stent is estimated at about 3-7 weeks.
The Wilcoff U.S. Pat. No. 4,990,155 describes a plastic stent having an inherently expandable coil conformation. The "inherency" results from an elastic memory conferred by electron beam radiation imparting cross-linkages that provide an inherent tendency to return to a given diameter after any distortion. Materials of construction include high density polyethylene. Optionally, this material is compounded with an anti-coagulant and/or an x-ray opaque material such as bismuth-sub-carbonate.
The Shockley et al U.S. Pat. No. 4,994,033, describes a drug delivery dilatation catheter having three flexible, plastic tubes concentrically arranged relative to each other. The outermost sleeve of this catheter contains microholes for drug delivery. These microholes are made with a laser beam. Drugs that can be delivered by this system include aspirin, persantin, heparin, and prostaglandins. Drugs are delivered when externally applied pressure causes the innermost sleeve to balloon out. The drug is then forced through the microholes to spray and to treat a lesion.
Sigwart, Canadian Patent Application 2,008,312, describes a stent made from a malleable flat sheet having a reticulated pattern. The reticulated pattern includes non-deformable squares or diamonds. The stent is made by rolling the sheet and locking the sheet into a spiral having a small diameter. The sheet is locked into a spiral by a tie interwoven into the reticulated pattern. Once inserted into the lumen of a vessel, the spiral is expanded and held in place by flaps integrated into the outer body of the stent.
The stents mentioned do not remedy all problems relating to stents. In particular, some uses require stents to safely degrade within the bloodstream of an artery or vein over a period of weeks to months. Such stents must meet particular criteria. For instance, such stents must be compatible with surrounding tissue in the vein or artery as well as with blood flowing through the vein or artery. Degradation products must be prevented from forming emboli.
Stents should also optimize flow through a vein or artery. Additionally, there is a need for stents which deliver agents or drugs to blood passing through the vein or artery that are generally beneficial to the recipient. Also desired are stents which can deliver drugs or biologically active agents at a controlled rate to blood passing through the vessel lumen as well as to the vessel wall.